1. Field of the Invention
The present invention relates to an automatic seat belt system, and more particularly to an automatic seat belt system having a mechanism of adjusting the height of a webbing worn by a seat occupant of a vehicle.
2. Description of the Related Art
In an automatic seat belt system of this type, one end of a webbing is retained by a slider disposed movably along a guide rail. The slider is connected to a motor via an elongated flexible tape or a wire, and is adapted to move along the guide rail as the motor rotates.
A slider holding member (shoulder anchor) is disposed at one end portion of the guide rail on the rear side of the vehicle. The shoulder anchor has a lock shaft capable of engaging with the slider, and is connected to a reinforcing member of a side wall of a chassis via a lock pin. As the slider engages with the lock shaft, the slider is connected to and held by the reinforcing member via the lock pin. In addition, the shoulder anchor is so arranged that the position at which it is connected to the reinforcing member by means of the lock pin can be changed along the guide rail.
When a occupant is seated in a vehicle seat and the door is closed, the slide moves in the rearward direction of the vehicle along the guide rail as the motor is driven. When the slider reaches a predetermined position, the slider is brought into contact with the shoulder anchor and is held thereby, and the position at which the slider is held is detected by a limit switch, whereupon the driving of the motor is stopped. The occupant thus assumes a state in which the webbing is applied to him or her.
In addition, if the occupant alters the position at which the shoulder anchor is connected to the reinforcing member by means of the lock pin, it is possible to adjust the position at which the slider is held, i.e., the height of the webbing worn by the occupant. Thus, even if the occupant has a different physical constitution, the webbing can be applied properly around him or her.
With such a conventional automatic seat belt system having a mechanism for adjusting the height of the webbing worn, the motor is stopped if the slider is held by the shoulder anchor, as described above. However, even after the motor stops, the slider and the flexible tape move slightly owing to the inertia of these components and the motor. For this reason, at a point of time when the slider and the flexible tape are brought to a complete stop, load acting in the direction of movement of the slider owing to the movement of these members is applied to that portion of the shoulder anchor which is connected to the reinforcing member by means of the lock pin. Hence, the lock pin and the reinforcing member remain abutting against each other with this load acting on them.
Consequently, when the occupant temporarily cancels the connection between the lock pin and the reinforcing member by moving the shoulder anchor along the guide rail so as to adjust the height of the webbing worn, a large frictional force is generated between the lock pin and the reinforcing member. Hence, a large operating force becomes necessary, so that there has been a drawback in that the operational feature involved in adjusting the height of the webbing worn is undermined.